Spatial assessment of ecosystem resilience in the Asahan Toba watershed, Indonesia

Abstract This study examines the ecosystem resilience of the Asahan Toba Watershed in North Sumatra, Indonesia, employing an integrated spatial methodology. Resilience was evaluated using three principal biophysical indicators: vegetation density (assessed via the Normalized Difference Vegetation Index - NDVI), biodiversity index (Shannon-Wiener H’), and slope gradient, alongside an analysis of regional accessibility as a surrogate for anthropogenic pressure. The research employed Geographic Information Systems (GIS) and multiple linear regression to determine how each variable influenced the outcome and its corresponding weight. The findings demonstrate that NDVI is the predominant factor, accounting for 59.4% of the resilience model, followed by accessibility at 26.0% and slope at 14.6%. Spatial analysis revealed that the watershed is predominantly composed of areas with high (43.9%) and medium (20.4%) levels of resilience. Low-resilience areas were mostly found in parts of Asahan, Toba, and North Tapanuli regencies. They had little vegetation cover, were easily accessible, and featured steep slopes. Model validation demonstrated a 70% agreement between the predicted resilience levels and the biodiversity data obtained from the field. The research indicates that the Asahan Toba watershed has a relatively high chance of being spatially resilient. However, to maintain healthy ecosystems and ensure that essential hydrological and ecological functions remain intact, targeted conservation and rehabilitation efforts are necessary in vulnerable areas.